Carbon-based fine structure array, aggregate of carbon-based fine structures, use thereof and method for preparation thereof

ABSTRACT

An aggregate of carbon-based fine structures in which a plurality of carbon-based fine structures are collected, wherein respective carbon-based fine structures are oriented in the same direction. The above aggregate of carbon-based fine structures is an aggregate of a plurality of carbon-based fine structures in a state they are pulled by one another with strong interaction, and has such a length that allows the improvement of the handleability and workability thereof.

TECHNICAL FIELD

The present invention relates to a carbon-based microstructure array, anaggregate of carbon-based microstructures, use thereof, and afabrication method thereof. More specifically, the invention relates toan array of carbon-based microstructures, for example, such as carbonnanotubes, and an aggregate of carbon-based microstructures that areheld together by strong interactions such as van der Waals forces. Theinvention also relates to various uses of such array and aggregate ofcarbon-based microstructures, and a fabrication method thereof.

BACKGROUND ART

Carbon nanotubes (hereinafter, “CNTs”), one type of carbon-based microstructure, are carbon material that take the form of a pipe, with adiameter ranging from about 0.5 nm to about 10 nm, and a length of about1 um. CNTs were first discovered as a new carbon material by S. Iijimaof NEC in 1991. There are two types of CNTs: single-walled nanotubes ofa single-layer structure, and multi-walled tubes of a multi-layerstructure.

However, due to the microstructure, CNTs are difficult to handle andprocess. As such, there have been attempts to fabricate CNTs of a sizelarge enough to be handled under naked eye (see Non-Patent Publications1 and 2, for example).

Non-Patent Publications 1 and 2 report CNTs that are longer thanconventional CNTs of about 1 μm. The CNTs taught in Non-PatentPublication 1 is about 10 cm to about 20 cm long, and the CNTs taught inNon-Patent Publication 2 is about 25 cm to about 30 cm long. These CNTscan therefore be observed by naked eye.

CNTs exhibit metal-like properties or semiconductor-like propertiesdepending on their compositions. There accordingly has been activedevelopment of products or fabrication methods that take advantage ofsuch properties of CNTs. Potential use of CNTs as a hydrogen absorbingmaterial, as well as applications of CNTs to fuel cell, have also beenstudied.

As an example of material applications of CNTs, a woven fabric or asheet has been proposed that uses CNTs (see Patent Publication 1, forexample). Patent Document 1 describes using CNTs as part of a fiber or ayarn, or a fiber or a yarn itself, and using such fiber or yarn for awoven fabric or a sheet.

(Patent Publication 1) Japanese Laid-Open Patent Publication No.138838/1995 (published on May 30, 1995)

(Non-Patent Publication 1) H. W. Zhu, and 5 others, “Direct Synthesis ofLong Single-Walled Carbon Nanotube Strands”, Science, May 3, 2002, Vol.296, p. 884-886

(Non-Patent Publication 2) Kaili Jiang, and 2 others, “Spinningcontinuous carbon nanotube yarns”, Nature, Oct. 24, 2002, Vol. 419, p.801

The CNTs described in Non-Patent Publication 1 are about 10 cm to 20 cmlong. However, the CNTs disclosed in this publication cannot be formedeasily.

The CNTs described in Non-Patent Publication 2 are fabricated from CNTsthat take the form of a brush. Specifically, a plurality of CNTs areformed on a substrate by being aligned in a direction perpendicular tothe substrate. The CNTs are then detached from the substrate in bundlesand pulled away.

In such aggregate of CNTs, neighboring CNTs are entangled as a CNT ispulled out from the brush-like CNTs. The brush-like CNTs are thereforerequired to be made out of CNTs that are sufficiently long and areformed in high density.

However, in a conventional fabrication method of brush-like CNTs, theCNTs can be grown on the substrate only slowly and brush-like CNTs withlong aligned CNTs cannot be obtained. Further, due to the slow growthrate of CNTs, the conventional method is disadvantageous in terms ofproductivity.

Another drawback of the conventional method is that the CNTs cannot beformed in high density. The brush-like CNTs therefore fail to provideenough interactions for entangling neighboring CNTs together. It istherefore difficult to obtain rope-like CNTs.

The present invention was made in view of the foregoing problems, and anobject of the present invention is to provide an array of carbon-basedmicrostructures, and an aggregate of carbon-based microstructures thatare held together by strong interactions and are long enough to improveease of handling and workability. The invention also provides varioususes and a fabrication method of such array and aggregate ofcarbon-based microstructures.

DISCLOSURE OF INVENTION

The inventors of the present invention diligently worked to solve theforegoing problems, and found that CNTs that are held together by stronginteractions could be obtained by constructing brush-like CNTs from longCNTs that are forested in high density. The present invention was madebased on this finding.

Specifically, according to the present invention, there is provided anaggregate of carbon-based microstructures, which includes a plurality ofcarbon-based microstructures that are assembled together, wherein thecarbon-based microstructures are aligned in one direction, and areassembled together along the direction of alignment.

The aggregate of carbon-based microstructures is an assembly ofcarbon-based microstructures and is therefore very strong. Further,since the carbon-based microstructures are aligned in one direction, theaggregate has superior alignment. As used herein, “aligned in onedirection” refers to the alignment of all carbon-based microstructuresheld together with their lengthwise directions pointing the samedirection. The carbon-based microstructures are not always linear butare often curved slightly. As such, the “lengthwise direction” refers toa direction from one end to the other end of the carbon-basedmicrostructure, i.e., the direction of extension of the carbon-basedmicrostructures.

Further, since the carbon-based microstructures are assembled togetheralong the direction of alignment, the carbon-based microstructures canbe made longer. In this way, the size of the aggregate can be increasedto the extent where the aggregate can be observed by naked eye, and as aresult ease of handling and workability can be improved.

As described above, an aggregate of carbon-based microstructuresaccording to the present invention is structured such that a pluralityof carbon-based microstructures are aligned in one direction and areassembled together along the direction of alignment. This improves thealignment and strength of the aggregate.

According to the present invention, there is provided an array ofcarbon-based microstructures, which includes carbon-basedmicrostructures that are provided on a substrate by being alignedsubstantially perpendicular to the substrate, wherein the carbon-basedmicrostructures are provided on the substrate at a density of no lessthan 1×10¹¹/cm².

An array of carbon-based microstructures is made up of a plurality ofcarbon-based microstructures formed on a substrate, and the carbon-basedmicrostructures are aligned in a direction substantially perpendicularto the substrate. This enables the carbon-based microstructures to bedensely packed together to form an array.

In an array of carbon-based microstructures, the carbon-basedmicrostructures are provided on the substrate at a density of no lessthan 1×10¹¹/cm². In other words, an array of carbon-basedmicrostructures includes carbon-based microstructures that are verydensely packed together. As used herein, “substantially perpendicular”to the substrate means almost perpendicular to the substrate. Themeaning of “substantially perpendicular” includes a direction completelyperpendicular to the substrate, as well as directions away from thesubstrate.

According to the present invention, there is provided a fabricationmethod of an aggregate of carbon-based microstructures, the methodincluding the steps of: forming a plurality of carbon-basedmicrostructures on a substrate with a direction of alignmentperpendicular to the substrate; and pulling at least one of thecarbon-based microstructures.

According to this arrangement, a plurality of carbon-basedmicrostructures are formed perpendicular to the substrate, and at leastone of the carbon-based microstructures is pulled out. Since thecarbon-based microstructure is pulled out from ones that are aligned inone direction, unidirectional alignment can be realized. Further, sinceneighboring carbon-based microstructures are drawn out together in abundle, the alignment and ease of bundling of the aggregate can beimproved. As a result, a long and strong aggregate can be realized.

As described above, in a fabrication method of carbon-basedmicrostructures according to the present invention, a plurality ofcarbon-based microstructures are formed and at least one of thecarbon-based microstructures is pulled out. This improves the alignment,ease of bundling, and strength of the aggregate, and the length of theaggregate can be increased as well.

Additional objects, features, and strengths of the present inventionwill be made clear by the description below. Further, the advantages ofthe present invention will be evident from the following explanation inreference to the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1( a) is a photograph (image) showing a CNT rope, according to oneembodiment of the present invention.

FIG. 1( b) is a photograph (image) showing a CNT rope, according to oneembodiment of the present invention.

FIG. 2 is a cross sectional view schematically showing a device used tofabricate brush-like CNTs, according to one embodiment of the presentinvention.

FIG. 3 is a block diagram showing steps of fabricating the brush-likeCNTs, according to one embodiment of the present invention.

FIG. 4 is a diagram showing a relationship in the flow rates of carriergas and source gas, according to one embodiment of the presentinvention.

FIG. 5 is a graph representing a correlation between source gasconcentration and growth rate, according to one embodiment of thepresent invention.

FIG. 6( a) is a photograph (image) showing a scanning electronmicroscope (SEM) image of brush-like CNTs, according to one embodimentof the present invention.

FIG. 6( b) is a photograph (image) showing a scanning electronmicroscope (SEM) image of brush-like CNTs, according to one embodimentof the present invention.

FIG. 7( a) is a photograph (image) showing a CNT rope, according to oneembodiment of the present invention.

FIG. 7( b) is a photograph (image) showing a CNT rope, according to oneembodiment of the present invention.

FIGS. 8( a) through 8(d) are photographs (images) showing scanningelectron microscope (SEM) images of a CNT rope, according to oneembodiment of the present invention.

FIG. 9 is a photograph (image) showing a CNT sheet, according to oneembodiment of the present invention.

FIG. 10( a) is a photograph (image) showing a scanning electronmicroscope (SEM) image of brush-like CNTs, according to one embodimentof the present invention.

FIG. 10( b) is a photograph (image) showing a scanning electronmicroscope (SEM) image of brush-like CNTs, according to one embodimentof the present invention.

FIG. 10( c) is a photograph (image) showing a scanning electronmicroscope (SEM) image of a CNT rope, according to one embodiment of thepresent invention.

FIG. 10( d) is a photograph (image) showing a scanning electronmicroscope (SEM) image of a CNT rope, according to one embodiment of thepresent invention.

FIG. 11( a) is a photograph (image) showing how the CNT rope is lifted,according to one embodiment of the present invention.

FIG. 11( b) is a photograph (image) showing how the CNT rope is lifted,according to one embodiment of the present invention.

FIG. 12 is a photograph (image) showing a sample being observed tomeasure electrical properties.

FIG. 13( a) is a diagram showing steps of fabricating a pre-preg and alaminate, according to one embodiment of the present invention.

FIG. 13( b) is a diagram showing steps of fabricating a pre-preg and alaminate, according to one embodiment of the present invention.

FIG. 13( c) is a diagram showing steps of fabricating a pre-preg and alaminate, according to one embodiment of the present invention.

FIG. 14 is a photograph (image) showing a coiled structure with a rolledCNT rope, according to one embodiment of the present invention.

FIG. 15( a) is photograph (image) showing a transmission electronmicroscope (TEM) image of brush-like CNTs, according to one embodimentof the present invention.

FIG. 15( b) is a photograph (image) showing a transmission electronmicroscope (TEM) image of conventional brush-like CNTs.

FIG. 16( a) is a photograph (image) showing a transmission electronmicroscope (TEM) image of brush-like CNTs, according to one embodimentof the present invention.

FIG. 16( b) is a photograph (image) showing a transmission electronmicroscope (TEM) image of brush-like CNTs, according to one embodimentof the present invention.

FIG. 17( a) is a photograph (image) showing how the strength of a CNTrope is measured, according to one embodiment of the present invention.

FIG. 17( b) is a photograph (image) showing how the strength of a CNTrope is measured, according to one embodiment of the present invention.

FIG. 17( c) is a photograph (image) showing how the strength of aconventional CNT rope is measured.

FIG. 17( d) is a photograph (image) showing how the strength of aconventional CNT rope is measured.

FIG. 18 is a graph representing a relationship between CNT density ofthe brush-like CNTs and length of the CNT rope.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will describe one embodiment of the present invention. Itshould be appreciated that the present invention is not limited in anyway by the following description.

The present invention is an aggregate of carbon-based microstructures(hereinafter referred to as an “aggregate”), which are aligned in onedirection and are assembled together along the direction of alignment.The meaning of an aggregate according to the present invention alsoincludes carbon-based microstructures that are assembled togetherorthogonal to the direction of alignment. In order to fabricate anaggregate according to the present invention, a multiplicity ofcarbon-based microstructures is formed on a substrate by being alignedin a direction substantially perpendicular to the substrate, and atleast one of the carbon-based microstructures is pulled out. Thefollowing describes this in detail.

[Carbon-Based Microstructures]

Carbon-based microstructures are nanoscale structures composed of carbonatoms, with a network of carbon atoms building a backbone structure.More specifically, carbon-based microstructures have a three-dimensionalbonding structure similar to that of graphite. Preferably, thethree-dimensional structure is a cylinder.

Carbon nanotubes (hereinafter simply “CNTs”) are one specific example ofsuch carbon-based microstructures. Other examples of carbon-basedmicrostructures include CNTs with beads, a carbon nano-twist withtwisted CNTs, a carbon nano-coil, and fullerenes with a spherical shellstructure. As used herein, the term “an array of carbon-basedmicrostructures” may be used to refer to brush-like CNTs, in which largenumbers of carbon-based microstructures, CNTs, are forested together.

An aggregate according to the present invention is fabricated withbrush-like CNTs, as will be described later. As such, the followingdescription will be given through the case where carbon-basedmicrostructures are CNTs, and an array of carbon-based microstructuresis made up of brush-like CNTs, for example.

[An Array of Carbon-Based Microstructures]

Brush-like CNTs include a plurality of CNTs that are forested on asubstrate and are aligned in a direction substantially perpendicular tothe substrate. The substrate may be made from a Si wafer with a Fe thinfilm formed thereon as a catalyst. As used herein, “substantiallyperpendicular” to the substrate means almost perpendicular to thesubstrate, though it is preferably perfectly perpendicular. The meaningof “substantially perpendicular” also includes directions away from thesubstrate.

Brush-like CNTs according to the present invention are preferably madeout of CNTs that extend a certain distance in length (height) and aredensely formed on the substrate. With the CNTs of a certain lengthformed on the substrate, a long aggregate can be formed in thefabrication process. Specifically, the brush-like CNTs are preferablymade out of CNTs that extend at least several micrometers in length.

Further, with the CNTs densely formed together, neighboring CNTs can beheld together with strong interactions, for example, by van der Waalsforces. For example, the brush-like CNTs are preferably made out of 10or more CNTs that are formed in each 1 μm² area of the substrate. Inother words, the CNTs are preferably formed at a density of at least 10CNTs/μm² (1×10⁹ CNTs/cm²).

As described above, an aggregate according to the present invention isformed from brush-like CNTs. Though detailed explanations will follow,the length of the aggregate can be increased by increasing the densityof the CNTs in the brush-like CNTs. It is therefore preferable that theCNTs in the brush-like CNTs be formed at a density of at least 1×10¹⁰CNTs/cm², or particularly preferably at least 1×10¹¹ CNTs/cm².

Further, it is preferable that the brush-like CNTs be made out of CNTsthat have good crystallinity. The CNTs can have a more linear structureas the level of crystallinity is improved. By improving linearity of theCNTs, the aggregate can be formed more easily. That is, it is ideal thatthe CNTs be linear in shape, and any defect in the crystalline structureof the CNTs should be avoided since it causes a bend in the CNTs.

As used herein, “defects” are irregular portions in an ordered crystalarrangement of CNTs. The CNTs are made up of (flat hexagonal) graphenesheets of six-membered rings of carbon atoms. Defects occur if nonsix-membered rings, for example, such as five-membered rings orseven-membered rings, occur in portions of such orderly arranged crystalarray.

The CNTs assume a linear structure when the six-membered rings arearranged in an orderly fashion. However, if five- or seven-memberedrings are present in portions of the array, crystallinity suffers andthe CNTs are bent in these (defect) portions. Thus, the linearity of theCNTs can be desirably improved by reducing defects. As used herein, CNTswith a few defects refer to CNTs that include no more than 10 defects ina portion 1 μm long, for example.

Crystallinity also suffers when the crystal array of CNTs containsamorphous carbon, or when layers of amorphous carbon are formed aroundthe CNTs. Thus, CNTs with a smaller number of amorphous carbon atomshave better crystallinity.

FIG. 15( a) shows a TEM image of CNTs according to the presentinvention, and FIG. 15( b) shows a TEM image of conventional CNTs. Ascan be seen in FIGS. 15( a) and 15(b), the number of amorphous carbonatoms that occur around the CNTs are considerably smaller in the CNTsaccording to the present invention than in the conventional CNTs. Thisaccounts for the poor linearity of the conventional CNTs withirregularly curved graphene sheets. On the other hand, the CNTsaccording to the present invention have a structure with orderly layeredgraphene sheets, providing excellent crystallinity.

The thickness of the amorphous carbon layer formed around the CNTs ispreferably no greater than 10% of the diameter of the CNTs. This furtherimproves linearity of the CNTs.

As described above, CNTs with high crystallinity have high linearity.The high linearity improves the interactions between the CNTs. With thebrush-like CNTs including CNTs with high crystallinity, a strongaggregate can easily be produced. CNTs with superior crystallinity andlinearity can be produced by a fabrication method according to thepresent invention, as will be described later.

Preferably, the CNTs include graphene sheets in a range of 2 to 20layers, inclusive. By increasing the number of graphene sheet layers,the strength of the aggregate formed in a subsequent step can beincreased. However, if the number of graphene sheet layers exceeds 20,the aggregate loses flexibility and may break apart when a certainamount of force is applied.

[Fabrication Method of an Array of Carbon-Based Microstructures]

Brush-like CNTs according to the present invention can be fabricated bya CCVD (catalyst chemical vapor deposition) method. CCVD is a methodwhereby a catalyst is placed in a reaction chamber, which is thencharged with carrier gas and source gas to grow CNTs on the surface ofthe catalyst. The following describes how the brush-like CNTs arefabricated by growing CNTs according to the CCVD method.

FIG. 2 is a diagram schematically illustrating a device 1 used for thefabrication of the brush-like CNTs. As shown in FIG. 2, a catalyzer 3 isplaced in a reaction chamber 2. The catalyzer 3 is a base material witha catalyst placed thereon. The base material may be provided in variousforms, for example, such as a substrate, a multi-layered substrate, acylinder, a polyhedron, a pellet, and a powder. As a catalyst, varioustypes of conventional catalysts can be used, examples of which includeiron, cobalt, nickel, an iron alloy, a cobalt alloy, a nickel alloy,iron oxides, cobalt oxides, nickel oxides, and combinations of thesecatalysts.

The reaction chamber 2 is charged with carrier gas and source gas. FIG.3 shows how carrier gas and source gas are supplied to the reactionchamber 2 in steps. The carrier gas is stored in a first container 4 anda second container 5. The carrier gas in the first container 4 issupplied to the reaction chamber 2 after a basic flow rate has been setby a first flow-rate control unit 6 realized by a mass flow controller.The carrier gas in the second container 5 is supplied to the reactionchamber 2 via an electromagnetic three-way valve 8 after a predeterminedflow rate has been set by a second flow-rate control unit 7 realized bya mass flow controller.

The carrier gas may be He, Ne, Ar, N₂, or H₂, for example. The carriergas is used to carry the source gas, and it, unlike the source gas, doesnot undergo any reaction and is not consumed.

The source gas is contained in a third container 9. The source gas inthe third container 9 is supplied to the reaction chamber via anelectromagnetic three-way valve 11 after a predetermined flow rate hasbeen set by a third flow-rate control unit 10 realized by a mass flowcontroller.

The source gas may be organic gas such as hydrocarbon gas,sulfur-containing organic gas, or phosphorus-containing organic gas. Thetype of source gas is suitably selected according to the structure ofCNTs to be produced. Among these exemplary organic gases, hydrocarbongas can be preferably used because it does not generate wastesubstances.

The hydrocarbons may be, for example, alkane compounds such as methaneand ethane; alkene compounds such as ethylene and butadiene; alkynecompounds such as acetylene; aryl hydrocarbon compounds such as benzene,toluene, and styrene; aromatic hydrocarbons with a condensed ring, suchas indene, naphthalene, and phenanthrene; cycloparaffin compounds suchas cyclopropane and cyclohexane; cycloolefin compounds such ascyclopentene; aliphatic hydrocarbon compounds with a condensed ring,such as steroid. Further, a hydrocarbon gas with a mixture of two ormore of these hydrocarbon compounds may also be used. Among theseexemplary hydrocarbon compounds, particularly preferable are acetylene,allylene, ethylene, benzene, and toluene.

Under the control of an automatic valve control unit, theelectromagnetic three-way valves 8 and 11 are switched between closedstate and supply state. Specifically, in the closed state, the carriergas and source gas are emitted via an auxiliary exhaust pipe. In thesupply state, the carrier gas and source gas are supplied to thereaction chamber. When the electromagnetic three-way valve 8 is in thesupply state, the electromagnetic three-way valve 11 is in the closedstate. When the electromagnetic three-way valve 8 is in the closedstate, the electromagnetic three-way valve 11 is in the supply state.

The electromagnetic three-way valves 8 and 11 have a response time thatdoes not exceed 0.1 s. The flow rate of the carrier gas supplied to thereaction chamber 2 from the first container 4 is controlled at a basicflow rate at all times. The flow rate of the carrier gas supplied to thereaction chamber 2 from the second container 5 and the flow rate of thesource gas supplied to the reaction chamber 2 from the third container 3are controlled to always have the same flow rate. As such, the switchingbetween closed state and supply state is made instantaneously so thatthe flow rates of gases supplied to the reaction chamber 2 remainconstant at all times.

For example, assume that the basic flow rate of the carrier gas suppliedfrom the first container 4 is X (cm³/s (normal)), and that the flow rateof the carrier gas supplied from the second container 5 and the flowrate of the source gas supplied from the third container 9 are Y (cm³/s(normal)).

As shown in FIG. 4, the reaction chamber 2 is always charged with thecarrier gas supplied from the first container 4 (cm³/s (normal)). Whenthe brush-like CNTs are not produced, the electromagnetic three-wayvalve 8 is in the supply state and the electromagnetic three-way valve11 is in the closed state. In this case, since the carrier gas from thesecond container 5 is supplied at flow rate Y (cm³/s (normal)), thereaction chamber 2 is charged with gases at the flow rate of X+Y (cm³/s(normal)).

On the other hand, when the brush-like CNTs are produced, theelectromagnetic three-way valve 8 is in the closed state and theelectromagnetic three-way valve 11 is in the supply state. In this case,since the source gas from the third container 9 is supplied at flow rateY (cm³/s (normal)), the reaction chamber 2 is charged with gases at theflow rate of X+Y (cm³/s (normal)), as in the foregoing case. That is,the flow rates of gases supplied to the reaction chamber 2 remainconstant at all times.

The reaction chamber 2 is heated to optimum temperatures for CNT growth,and the source gas undergoes pyrolysis in the vicinity of the catalyzer3. The decomposed product of pyrolysis then grows into CNTs on thesurface of the catalyzer 3.

The following specifically describes the method by which the brush-likeCNTs are produced with the device 1. As the catalyzer (substrate) 3, aSi substrate with an iron catalyst film of 4 nm thick formed thereon isused. As the carrier gas and source gas, He gas and C₂H₂ gas are used,respectively. The basic flow rate of the He gas from the first container4 is set to 0.93 cm³/s (normal), and the flow rate of the He gas fromthe second container 5 and the flow rate of the C₂H₂ gas from the thirdcontainer 9 are set to 3.11 cm³/s (normal).

First, the substrate 3 is placed in a middle portion of the reactionchamber 2, which is then heated to 700° C. Here, the electromagneticthree-way valve 8 is in the supply state, and the reaction chamber 2 ischarged with He gas at the flow rate of 4.04 cm³/s (normal). Theelectromagnetic three-way valve 8 is then closed, and, at the same time,the electromagnetic three-way valve is opened. As a result, the reactionchamber 2 is charged with C₂H₂ gas and He gas at the flow rates of 3.11cm³/s (normal) and 0.93 cm³/s (normal), respectively. Here, the C₂H₂ gashas a concentration of 76.9%, and is supplied for 0.8 seconds. Thereaction chamber 2 is then heated for 5 minutes after the C₂H₂ gas hasbeen supplied, by which time the C₂H₂ gas has passed the reactionchamber 2. As a result, carbon atoms in C₂H₂ grow on the substrate 3 andthe brush-like CNTs are formed.

Referring to FIG. 5, the following describes a relationship betweengrowth rate of CNTs and concentration of source gas in the fabricationof the brush-like CNTs. As shown in FIG. 5, the growth rate of CNTsincreases with increase in concentration of the source gas. Theincreasing growth rate of CNTs can be explained by the rapid change inthe concentration of the source gas upon reaching the substrate. Byincreasing the growth rate of CNTs, the work time can be reduced and theCNTs can be extended in length.

Increasing the concentration of the source gas from 23% to 76.9%increases the density of CNTs from 2×10¹⁰/cm² to 7×10¹¹/cm². That is,the density of CNTs can be increased by increasing the concentration ofthe source gas.

It is therefore preferable that the concentration of the source gas usedto fabricate the brush-like CNTs be no less than several ten percent.Specifically, the concentration of the source gas is preferably in arange of 23% to 70%, inclusive. This enables the CNTs to grow bothquickly and densely.

The growth time of CNTs can be increased by extending the supply time ofthe source gas. In other words, by controlling the supply time of thesource gas, the length of CNTs can be increased even longer. However,since there is a corresponding increase in the diameter of the CNTS inthis case, the supply time of the source gas should be suitably decidedtaking into account the concentration of the source gas and requiredlength and thickness of CNTs. Preferably, the supply time of the sourcegas is in a range of 0.001 seconds to 60 seconds.

FIGS. 6( a) and 6(b) show scanning electron microscope (SEM) images ofthe brush-like CNTs. FIG. 6( b) is a magnified view of FIG. 6( a). Ascan be seen in FIGS. 6( a) and 6(b), the CNTs of the brush-like CNTs arehighly linear and have grown to about 170 μm in length. The density ofthe CNTs was estimated to be at least 1×10¹⁰/cm².

In the present embodiment, the measurement of CNT density is performedas follows based on SEM and TEM images.

First, portions of CNTs exhibiting the same contrast in the SEM imageare examined as shown in FIG. 6( a) or 6(b). As used herein, “portionsexhibiting the same contrast” or “the same contrast portions” refers toportions of SEM image where intensities of the CNTs are substantiallyuniform. Such portions are estimated to have a substantially constantCNT density.

Then, the widths of CNTs in the same contrast portions are measured.From the result of measurement, the diameters of CNTs in the samecontrast portions can be estimated. Further, the number of CNTs in thesame contrast portions is also measured to estimate the density of CNTstherein. It should be noted that since the CNTs that appear in the SEMimage are bundles of CNTs (bundle CNTs), the estimated density in theSEM image is based on the number of bundle CNTs per unit area.

Then, portions of CNTs with estimated diameters and densities areobserved with TEM. FIGS. 16( a) and 16(b) show TEM images of the CNTs.As can be seen in the TEM images, the bundle CNTs observed in the SEMimages are indeed made up of individual CNTs. By observing the TEMimages, the number of CNTs in each bundle CNT is measured in the SEMimages.

Once the diameter of CNTs and the number of bundle CNTs in the samecontrast portions were measured in the SEM image, the number of CNTscontained in the bundle CNTs can be measured in the TEM image to givethe number of CNTs per unit area, i.e., CNT density.

A fabrication method according to the present invention enablesfabrication of the CNTs with high crystallinity, as well as thebrush-like CNTs made out of the CNTs with high crystallinity.

[Aggregate of Carbon-Based Microstructures]

In the following, description is made as to an aggregate of carbon-basedmicrostructures according to the present invention. An aggregateaccording to the present invention is made up of CNTs that are alignedin one direction and are assembled together along the direction ofalignment. As used herein, “aligned in one direction” refers to thealignment of all carbon-based microstructures that are assembledtogether with their lengthwise directions pointing the same direction.The carbon-based microstructures are not always linear but are oftencurved slightly. As such, the “lengthwise direction” refers to adirection from one end to the other end of the carbon-basedmicrostructure, i.e., the direction of extension of the carbon-basedmicrostructures.

An aggregate according to the present invention is made up of bundles ofCNTs tangled together. As such, an aggregate according to the presentinvention has such a structure that the bundles of CNTs that are alignedin the same direction extend along the lengthwise direction. Forconvenience of explanation, such structure will be referred to as a “CNTrope.”

Further, an aggregate according to the present invention also includesstructures that are assembled together along a direction orthogonal tothe direction of alignment. As used herein, a “direction orthogonal tothe direction of alignment” is a direction that is right angle to thelengthwise direction of the CNT ropes (transverse direction). That is,the CNT ropes can be aligned along both the lengthwise direction and thetransverse direction, and the aggregate can therefore have atwo-dimensional spread. Such structure can be described as an aggregatewith the CNT ropes that are assembled together along the sides of atwo-dimensional plane. For convenience of explanation, such aggregatewill be referred to as a “CNT sheet.”

FIGS. 1( a) and 1(b) and FIGS. 7( a) and 7(b) show CNT ropes accordingto the present invention, wherein FIGS. 1( a) and 1(b) show a CNT ropeabout 20 cm long, and FIGS. 7( a) and 7(b) a CNT rope about 30 cm long.As clearly shown in these Figures, a CNT rope according to the presentinvention is a yarn-like material that can be recognized by naked eye.

The following describes a detailed structure of the CNT rope. FIG. 8shows a SEM image of the CNT rope shown in FIGS. 1( a) and 1(b). FIGS.8( b) and 8(c) are SEM images magnifying portions of the CNT rope shownin FIG. 8( a), and FIG. 8( d) is a SEM image magnifying a portion of theCNT rope shown in FIG. 8( c).

As shown in FIG. 8, the CNT rope is a bundle of CNTs. In other words,individual CNTs are bundled together to make up the CNT rope. Theaverage diameter of the CNT rope is about 50 μm. The diameter ofindividual filamentous structures forming the CNT rope is about 50 nm.The diameter of individual CNT of the brush-like CNTs, as observed witha transmission electron microscope (TEM) is about 10 nm to about 20 nm.This supports the notion that the CNT rope is indeed a bundle ofindividual CNTs.

While the average length of individual CNTs in the brush-like CNTs isabout several ten micrometers, a CNT rope according to the presentinvention can be made as long as 20 cm or 30 cm. By controlling thedensity of CNTs in the brush-like CNTs, the length of the CNT rope canbe extended to 50 cm or even longer. This is possible because individualCNTs are bundled together by being aligned in the same direction alongthe lengthwise directions. Briefly, a CNT rope according to the presentinvention is a bundle of individual CNTs that are aligned in onedirection.

The CNTs in the bundle are partially held together by van der Waalsforces. Accordingly, the CNTs are held together by strong interactions,and as such the CNP rope is very strong. Further, the CNTs in the bundlecan be held together by physical or chemical means. In this case, thestrength of the CNP rope can be improved even further.

The CNT sheet is a two-dimensional aggregate of the CNT ropes, i.e., asheet of CNT ropes. As such, the CNT sheet is structured from thebundles of individual CNTs. However, in the CNT sheet, the individualCNTs that are aligned in one direction are continuously bundled togethernot only in the lengthwise direction but in the transverse direction aswell. FIG. 9 shows a CNT sheet. As can be seen in FIG. 9, the CNT sheetis in the form of a sheet with a width of 4 mm.

A CNT rope according to the present invention is fabricated using thebrush-like CNTs including highly crystalline CNTs. This renders the CNTrope very crystalline. The CNT rope is therefore highly linear. Further,with the densely formed CNTs, the brush-like CNTs can be used to producelong and strong CNT ropes.

In the following, description is made as to strength of a CNT ropeaccording to the present invention. FIGS. 17( a) and 17(b) arephotographs (images) measuring a strength of a CNT rope according to thepresent invention. FIGS. 17( c) and 17(d) are photographs (images)measuring a strength of a conventional CNT rope. In FIGS. 17( a) and17(b) and FIGS. 17( c) and 17(d), the strength (mechanical property) ofthe CNT rope was measured according to a resonating method.

FIG. 17( a) shows a CNT rope of the present invention in rest. FIG. 17(b) shows the CNT rope in a resonating state. FIG. 17( c) shows aconventional CNT rope in rest. FIG. 17( d) shows the conventional CNTrope in a resonating state. As can be seen from FIG. 17( b) and FIG. 17(d), the CNT rope of the present invention resonates over a smaller rangeand is therefore stronger than the conventional CNT rope. In theresonating method, Young's modulus is given by the following equation:Y=(64π²ρ/1.875⁴)×(f _(o) ² L ⁴ /d _(o) ²)  (1)where f_(o) is the oscillating frequency, ρ the density, L the length,and d_(o) the outer diameter (>>the square of inner diameter).

Calculation of Young's modulus using Equation (1) yielded the followingresults: Y=0.1 (TPa) for the conventional CNT rope, and Y=0.8 (TPa) forthe CNT rope of the present invention. The examination of mechanicalproperty therefore showed that the conventional CNT rope (with manydefects and wide bends) has a small Young's modulus and is weak.

[Fabrication Method of an Aggregate of Carbon-Based Microstructures]

The following describes a fabrication method of a CNT rope according tothe present invention. The CNT rope can be fabricated from thebrush-like CNTs.

As described above, the brush-like CNTs are formed on a substrate.Fabrication of a CNT rope proceeds by dividing the substrate apart. Bydividing the substrate, portions of the CNTs are exposed. At least oneof the CNTs in the exposed portion is picked and pulled out withtweezers or the like. As the CNT is pulled out, neighboring CNTs aredrawn out together as a continuous yarn of tangled CNTs. The CNT ispulled out in the direction it is drawn out from the substrate.

The CNTs are held together by van der Waals forces. Thus, by drawing outat least one of the CNTs, neighboring CNTs are continuously drawn out ina bundle along with it. By pulling the CNTs further, a bundle of CNTsare obtained that defines a CNT rope.

In this manner, a CNT rope with the unidirectionally aligned CNTs can beobtained simply by pulling the unidirectionally aligned brush-like CNTsand continuously drawing out CNTs. This makes it easy to controlalignment of the CNTs.

In the fabrication of the CNT rope, the brush-like CNTs are successivelystripped off from an end of the substrate—a process similar tounraveling a yarn from a sweater. FIG. 10( a) is a SEM image of thebrush-like CNTs after the CNT rope has been fabricated. As shown in FIG.10( a), the CNTs have been detached and the underlying Si substrate isexposed.

The brush-like CNTs are in the form of a sheet near the substratesurface, with the CNTs aligned parallel to the substrate, as shown inFIG. 10( b). In the fabrication of the CNT rope, the CNTs in the sheetare bundled together and form a rope. FIGS. 10( c) and 10(d) show SEMimages of the CNT rope.

The CNT sheet can be fabricated by increasing the number of CNTs pulledout from the brush-like CNTs. As mentioned above, the brush-like CNTsare in the form of a sheet near the substrate surface, and therefore aCNT sheet can be fabricated simply by pulling a sheet of CNTs. A sheetsize can be suitably changed by varying the number of CNTs picked todraw out the CNTs.

Alternatively, the CNT sheet can be fabricated by pulling each piece ofthe substrate that has been split apart. By pulling the substrates, theCNTs formed on the respective substrates attract each other tocontinuously unravel the CNTs. As a result, a CNT sheet is fabricated inwhich the CNTs are aligned in one direction.

Note that, the CNT rope or CNT sheet forms different bundles dependingon the density of CNTs in the brush-like CNTs. Thus, by controlling thedensity of the brush-like CNTs according to the intended use of the CNTrope or CNT sheet, the CNT rope or CNT sheet can be obtained in desiredbundles.

The present invention uses the brush-like CNTs with dense CNTs, enablingthe length of the CNT rope or CNT sheet to be increased. The followingdescribes a relationship between CNT density of the brush-like CNTs andlength of the CNT rope. FIG. 18 is a graph representing a relationshipbetween CNT density of the brush-like CNTs and the length of a CNT ropethat can be drawn out from the brush-like CNTs.

As shown in FIG. 18, CNTs can be drawn out when the CNT density of thebrush-like CNTs is about 1×10⁹/cm². That is, fabrication of the CNT ropeis possible. The length of the CNT rope is increased by increasing theCNT density. With a CNT density exceeding 1×10¹⁰/cm², a CNT rope can befabricated that extends about 10 cm to about 40 cm in length.

With the foregoing fabrication method, the present invention can producebrush-like CNTs with a CNT density of 1×10¹¹/cm² or greater. As shown inFIG. 18, when the CNT density is 1×10¹¹/cm² or greater, a CNT rope canbe fabricated that extends 50 cm or greater in length.

That is, a fabrication method of the present invention enablesfabrication of brush-like CNTs in high density and excellentcrystallinity, which can then be used to fabricate a long and strong CNTrope.

The CNT rope or CNT sheet can also be fabricated by strongly bindingCNTs by various methods. For example, the CNTs can be bound together byphysical or chemical means. As described above, the CNTs are heldtogether by strong interactions such as van der Waals forces. By morefirmly binding the CNTs, the strength of resulting CNT ropes or sheetscan be improved.

Examples of a method for physically or chemically binding CNTs includeplying, high-temperature annealing, and chemical treatment. Plying is amethod in which the CNTs are firmly plied together. In high-temperatureannealing, CNTs are heated in various kinds of high-temperature gases.Chemical treatment refers to a method in which the CNTs are physicallyor chemically bound together by introducing fullerene or functionalarrays.

[Use of an Aggregate of Carbon-Based Microstructures]

Owning to the foregoing structures and properties, an aggregate ofcarbon-based microstructures according to the present invention has manyapplications. For example, the aggregate can be used as a laminatedmatrix structure, a metal carrier, a surface modifier, a plied-yarnstructure, a fabric structure, or a coiled structure. The aggregate canalso be used as a reinforcing material, an electrical wire, a conductingwire, a sensor, a transparent conductor, a blade, a motor, a transparentelectromagnetic wave absorber, a building material, a diaphragm, asliding member, an artificial muscle, clothes, a fishing line, aphoto-absorber, a reflector, a nonwoven fabric, an artificial dielectricmedium, ink, coatings, a heat-resistant material, or anabrasion-resistant material. The following specifically describes theseapplications.

(Laminated Matrix Structure)

A CNT rope and CNT sheet of the present invention are anisotropic. Assuch, by impregnating or mixing the CNT rope or sheet of the presentinvention with resin or other materials, a sheet-like mold product(pre-preg) with an aligned matrix can be produced.

A pre-preg can be produced as follows. First, as shown in FIG. 13( a), aCNT rope or sheet is processed into a film or a sheet. Then, as shown inFIG. 13( b), the CNT rope or CNT sheet is impregnated with liquid resinor a resin solution. By curing the resin or evaporating the solvent, apre-preg is obtained. When the CNT rope or CNT sheet is impregnated withresin, a resin sheet is obtained as a mold product.

The pre-preg is applicable to a reinforced resin sheet of carbon fiberor glass fiber. For example, the pre-preg is applicable to aerospaceindustry which imposes severe weight and performance requirements. Otherapplicable areas include auto-materials, small ships, and sports gear.

The pre-preg can be laminated to provide a laminated matrix structure,which is a laminate as shown in FIG. 13( c). In laminating thepre-pregs, any angle can be suitably set for the alignment angle of theCNTs in each sheet. By suitably varying the alignment angle inlaminating the pre-pregs, many different properties can be rendered tothe laminates, for example, such as structural strength, anisotropy, andgood heat conductivity.

A laminate using the CNT rope or CNT sheet can be made considerablythinner than conventional pre-pregs using glass fiber or carbon fiber.With the strength, electrical conductivity, heat conductivity, or otherproperties, such ultra-thin film is applicable not only to the field ofhigh-strength materials, but has potential applications, though tolimited extent, in laminated boards (for example, IC, CPU) of electricaldevices. Recent electrical devices have encountered the problem of heatradiation due to high integration and large capacity. It is expectedthat the problem of heat radiation in a laminated board can be relievedwhen a laminate with good heat conductivity is used as an anisotropicheat conductive film.

(Metal Carrier)

By supporting metal on the aggregate, a metal carrier with a largesurface area can be provided. Owning to the fact that the CNT rope orCNT sheet is a bundle of large numbers of unidirectionally aligned thinCNTs, the CNT rope and CNT sheet have a large specific surface area(m²/g). This enables a large amount of metal to be supported, andthereby enables production of materials that excel in performance,efficiency, and activity. Further, since the dimensions (diameter,length, etc.) of the tubes in the CNT rope are uniform, the metal can besupported with good dispersibility.

For example, a metal catalyst (fine particles) such as Pt, Pd, or Ni maybe supported on the CNT rope. In this case, the CNT rope can be used asa catalyst material that has superior performance, efficiency, andactivity, or as a gas reaction material such as a gas filter. When usedas a gas filter, a pressure loss (gas resistance) can be reduced.Further, by supporting a fine particle metal such as Pt, the CNT ropecan be used as an electrode material for the fuel cell of a directmethanol type, for example. The energy density of the fuel cell can beimproved in this case.

The following describes an exemplary method of supporting Pt on CNTropes. First, an aqueous solution of platinic acid (H₂PtCl₆) issupplemented with H₂O₂ and NaHSO₃ to prepare a Pt colloid. The CNT ropesare then soaked one by one in the Pt colloid, and are heated for 5 to 7hours at 300° C. to remove Cl. The resulting CNT ropes are obtained asPt carriers.

Other than the gas filter, the metal carrier of the CNT rope or CNTsheet is can also be used as a molecular filter, a liquid filter, anoise-insulating filter, or a polarizing filter. The metal carrier ofthe CNT rope or CNT sheet is also applicable to various types ofabsorbent such as a gas absorbent.

The metal carrier of the CNT rope or CNT sheet can also be used as anelectrode. The electrode can be used as a fuel cell, a secondarybattery, or a super capacitor, for example. Since metal is supported oneach individual CNT rope with a large surface area, the amount of metalsupported on the CNT rope can be controlled. Further, in producing theelectrode material, metal can be supported more densely and moreuniformly in the electrode material by controlling intervals of the CNTropes. Further, design control of the electrode material is possible bycontrolling the rope diameter with different combinations of the CNTropes. This reduces the amount of supported metal, which enables thecapacitors to be designed with high energy density.

The electrode can be obtained by arranging the metal-supported CNT ropeson a PTFE (polytetrafluoroethylene) film, for example.

(Surface Modifier)

The surface of the aggregate may be modified to form a surface-modifiedyarn- or sheet-like material. As used herein, “modifying the surface”means binding an organic functional array or attaching (applying) afunctional thin film on a surface of the CNT rope or CNT sheet. Thisrenders the CNT rope or CNT sheet additional functionality.

Specifically, by chemically binding, for example, functional arrays,fullerene, or CNTs between the CNT ropes or CNT sheets, a yarn- orsheet-like material can be produced that excels in strength, electricalconductivity, heat conductivity, or other functionalities.

Examples of functional arrays include a nitro array (—NO2), a sulfonearray (—SO3H), a carboxyl array (—COOH), a carbonyl array (>C═O), anether array (C—O—C), and a phenolic hydroxy array (—OH). By suitablycombining CNT ropes or CNT sheets that have incorporated any of suchfunctional arrays, the CNT ropes or CNT sheets can be used as anion-exchange film, for example.

Further, for example, fullerene is known to undergo polymerization underplasma, light, electron beam, X-rays, or heat. Thus, by polymerizing thefullerene that has been incorporated between CNTs of the CNT ropes orCNT sheets, the functionality of the CNT ropes or CNT sheets can beimproved.

Further, such yarn- or sheet-like material may be combined (plied) intoa string or a sheet structure. Specifically, by plying the yarn-likematerial by chemical bonding, the strength and diameter can beincreased.

(Plied-Yarn Structure, Fabric Structure, Coiled Structure)

CNT ropes or CNT sheets of the present invention can be plied togetherto form a plied-yarn structure. This can be done by twisting around theCNT ropes or CNT sheets. A resulting plied-yarn structure is very strongand lightweight. The strength of the plied-yarn structure can beimproved further by using the surface-modified CNT ropes or CNT sheets.The plied-yarn structure may be provided as a string or a rope, forexample.

The plied-yarn structure can be plied further to fabricate a fabricstructure. Such a fabric structure can alternatively be fabricated byimpregnating the CNT ropes or CNT sheets with liquid resin or a resinsolution and plying them together. The fabric structure, then, is afabric-like or skin-like structure that is fabricated by braidingstrings or ropes of CNT ropes or CNT sheets, or CNT ropes or CNT sheetsthat have been impregnated with resin.

The CNT ropes or CNT sheets can be wound to fabricate a coiledstructure. For example, such coiled structure can be fabricated bywinding the CNT ropes or CNT sheets with a Bobbin®, as shown in FIG. 14.

(Reinforcing Material)

A CNT rope or CNT sheet of the present invention can be used as asheet-like or rope-like reinforcing material for carbon, FRP (FiberReinforced Plastics), FRM (Fiber Reinforced Metels), FRC (FiberReinforced Ceramics), C/C (Carbon/Carbon) composite, optical fibers, ortires, for example. A CNT rope or CNT sheet of the present invention canalso be used as a reinforcing material or composite material forceramics or metals, for example.

(Electrical Wires, Conducting Wires)

Common electrical wires are produced by plying copper lines into a thickwire. Conventionally, it has been difficult to fabricate long CNTs orlong plies of CNTs. In the present invention, the CNT ropes are pliedtogether, and therefore the length and thickness of the CNT rope can becontrolled. A CNT rope or CNT sheet of the present invention thereforehas potential applications as an electrical wire or a conducting wire.

The CNT has a smaller resistance than copper. The CNT rope and CNT sheetare therefore suitable as an electrical wire or conducting wire forhigh-resistant current. The CNT rope and CNT sheet have a greatercurrent density (current density per unit area) than copper. To takemulti-walled CNTs as an example, the maximum current density exceedsthat of copper by more than 1000 fold. Therefore, the CNT rope of thepresent invention is also applicable to LSI wiring. Further, a longconducting wire made out of the CNT rope would be useful when thin wiresare required to produce large current as in a large-torque/high-outputsmall motor. Further, since the CNT rope is lighter than conventionalmetal wires, the weight of the motor can be reduced by replacing thecopper wires with the CNT ropes.

Due to the small size, use of CNTs for the wiring of an electricaldevice is associated with difficulties in handling. However, byproviding the CNTs as a unidirectionally aligned aggregate as in thepresent invention, the CNTs can more easily be used as wirings. SuchCNTs can also be provided by being wound around a Bobbin®, for example.

It is generally believed that the upper limit of L/S of common thinlines currently in use is 10 microns. However, with the directional CNTrope or CNT sheet, a controllable range can be increased and nano-orderthin lines can be produced.

(Sensors)

A CNT rope and CNT sheet of the present invention can be used as asensor. The sensor may be a flow-rate sensor, a pressure sensor, or agas sensor, for example. The flow-rate sensor detects a flow rate bydetecting the amount of heat absorbed by the gas at a sensor unit. Thesize of the flow-rate sensor can be reduced by using the CNT rope or CNTsheet for the sensor unit. In this way, power consumption can bereduced. Further, a flow-rate sensor can be produced that can detecteven a trace flow rate.

A Pirani vacuum gauge is used a pressure sensor. In this particular typeof pressure sensor, changes in temperature of a filament due to heatenergy, which the gas molecules have taken away when they reflected offthe metal wires, are detected as changes in resistance. In the Piranivacuum sensor, the size and weight of the sensor can also be reduced byusing the CNT ropes or CNT sheets for the metal wires. Power consumptioncan be reduced as well. Further, with the CNT ropes or CNT sheets, thediameter of the filament can be reduced. This increases the measurablepressure range, and thereby enables fabrication of a wide-range vacuumgauge.

It is ideal that single-walled CNTs be used for the sensor unit of thegas sensor. However, CNT ropes or CNT sheets of CNTs with a small numberof layers can be used for the sensor unit. The CNTs are covered with πelectrons on sides. As such, polar gas molecules draw π electrons whenthey are absorbed by the CNTs. As a result, the electrical resistance ofthe CNT ropes or CNT sheets varies. The electrical resistance variesdifferently for different polarities of the gas molecules, therebyallowing for detection of different molecular species. Further, bymodifying the surfaces of CNTs with specific chemical molecules, it maybe possible to selectively detect different molecular species. The CNTrope and CNT sheet therefore have a potential use as a probe (detector).

(Transparent Electrodes)

A CNT rope and CNT sheet of the present invention are superior toconventional CNTs in terms of alignment and dispersibility, and aretherefore usable as a transparent material. For example, a CNT rope orCNT sheet with CNTs of controlled density may be installed in astructure to provide a transparent conductor. The transmittance orconductivity of the structure can be controlled according to the densityof the CNTs. Further, the CNT ropes or CNT sheets may be installed indifferent directions and stacked together to fabricate a device. Thestructure may be made of any material, including rubber and resin.

(Blades)

A CNT rope and CNT sheet of the present invention can be used as a bladeby taking advantage of high strength and nano-order sharpness.

(Small Motor, Small Electromagnet)

As described above, a CNT rope or CNT sheet of the present invention canbe used to fabricate conducting wires. The conducting wires can be usedto make a coil, which can then be used to fabricate a motor or anelectromagnet. The strength of magnetic field (related to the magnitudeof torque in a motor) in a motor or an electromagnet is proportional tothe number of turns or the magnitude of current in the coil. Thus, if anelectromagnet with a strong electric field were fabricated using copperwires, the size and weight of the electromagnet would be increased bythe thickness and weight of the copper wires. The size and weight of amotor or an electromagnet can be reduced greatly by using the CNT ropeor CNT sheet, which is thin, lightweight, and capable of flowing largecurrent.

(Film, Transparent Electromagnetic Wave Absorber, Building Material,Building Material, Diaphragm, Sliding Member, Artificial Muscle,Clothes)

A CNT rope or CNT sheet of the present invention can be processed tofabricate a thin film. The film can be used as a transparentelectromagnetic absorber. Further, a CNT rope and CNT sheet of thepresent invention are very strong, and have a specific gravity that issmaller than that of iron by about 10 fold. This makes the CNT rope andCNT sheet suitable for building materials. If the strength could beincreased further, it would be possible to use the CNT rope and CNTsheet as a material of a space elevator and the like.

Further, a CNT rope and CNT sheet of the present invention can be usedas a diaphragm. For example, by oscillating the CNTs, the CNT rope orCNT sheet can be used as a speaker. Further, by taking advantage ofsuperior alignment and ease of bundling, the CNT rope and CNT sheet ofthe present invention can be used as a sliding member for Pantograph® ofShinkansen®.

Further, with a powder of CNT applied over a double-sided tape and withelectrodes attached on the both sides of the tape, placing the tape in asaline solution and applying voltage causes the tape to bend. By takingadvantage of such property, the CNT rope or CNT sheet can be used as anartificial muscle of a nano-order diameter, by bonding two CNT ropestogether with a resin or other insulating layers in between. Further,such property can be exploited to realize a piezoelectric element.

Further, the CNT rope or CNT sheet can be used as a material of clothes.When used for this purpose, the CNT rope or CNT sheet providesprotection against electromagnetic wave or static electricity.

(Fishing Line, Photo-Absorber, Reflector, Nonwoven Fabric, ArtificialDielectric Medium, Ink, Coatings, Heat-Resistant Material,Abrasion-Resistant Material)

Other than the foregoing examples, a CNT rope and CNT sheet of thepresent invention can be used as fishing lines, photo-absorbers,reflectors, nonwoven fabrics, artificial dielectric Media, ink,coatings, heat-resistant materials, or abrasion-resistant materials. Bytaking advantage of superior alignment and dispersibility, the CNT ropeand CNT sheet can be used as a polarizing material. Thus, other thanpolarizing filters, the CNT rope and CNT sheet can be used asphoto-absorbers or the like.

When used as nonwoven fabrics, the thickness of the fabric can bereduced. When used as ink, conductive ink can be realized. When used ascoatings, the strength of the coating itself can be increased.

As described above, the present invention provides an aggregate ofcarbon-based microstructures, which includes a plurality of carbon-basedmicrostructures that are assembled together, wherein the carbon-basedmicrostructures are aligned in one direction, and are assembled togetheralong the direction of alignment.

In the aggregate of carbon-based microstructures, it is preferable thatthe carbon-based microstructures be assembled together in a directionorthogonal to the direction of alignment. By assembling the carbon-basedmicrostructures in a direction orthogonal to the direction of alignment,the aggregate can have a two-dimensional spread. This further improvesease of handling and workability.

In the aggregate of carbon-based microstructures, it is preferable thatthe carbon-based microstructures be bonded together by van der Waalsforces. Further, in the aggregate of carbon-based microstructures, it ispreferable that the carbon-based microstructures be physically orchemically bonded together. This makes it easier to assemble thecarbon-based microstructures, and thereby improves the strength of theaggregate.

In the aggregate of carbon-based microstructures, it is preferable thatthe carbon-based microstructures include no greater than 10 bends per 1μm length extending in the direction of alignment. This improvescrystallinity of the carbon-based microstructures. As a result, theaggregate can be made longer and the strength of the aggregate can beimproved. As used herein, a “bend” refers to a portion where thecarbon-based microstructures are bent from the direction of alignment.For example, a portion with a disordered crystal structure (known asdefects) constitutes a bend.

In the aggregate of carbon-based microstructures, it is preferable thatthe carbon-based microstructures be carbon nanotubes. Further, in theaggregate of carbon-based microstructures, it is preferable that metalbe supported on the carbon-based microstructures, and that thecarbon-based microstructures be surface-modified. This renders thecarbon-based microstructures a wide variety of additionalfunctionalities, allowing the carbon-based microstructures to be usedfor many different applications.

For example, the aggregate of carbon-based microstructures can be usedfor a reinforcing material, an electrical wire, a conducting wire, asensor, a transparent conductor, a blade, a motor, a building material,a diaphragm, a sliding member, an artificial muscle, clothes, a fishingline, a photo-absorber, a reflector, a nonwoven fabric, an artificialdielectric medium, ink, coatings, a heat-resistant material, or anabrasion-resistant material.

The carbon-based microstructures can also be used as a pliedyarn-structure realized by a ply of aggregates of carbon-basedmicrostructures; a fabric structure realized by a resin-impregnated plyof aggregates of carbon-based microstructures; or a coiled structurerealized by a roll of an aggregate of carbon-based microstructures.

The aggregate of carbon-based microstructures can also be used as aresin sheet realized by an aggregate of carbon-based microstructures. Alaminate can be obtained by stacking at least one resin sheet. The resinsheet or laminate can be used as a high-temperature conducting sheet.The aggregate can also be used as a film realized by an aggregate ofcarbon-based microstructures. The film can be used as a transparentelectromagnetic wave absorber.

As described above, the present invention provides an array ofcarbon-based microstructures, which includes carbon-basedmicrostructures that are provided on a substrate by being alignedsubstantially perpendicular to the substrate, wherein the carbon-basedmicrostructures are provided on the substrate at a density of no lessthan 1×10¹¹/cm².

In the array of carbon-based microstructures, it is preferable that thecarbon-based microstructures include no greater than 10 bends per 1 μmlength extending in the direction of alignment. This improvescrystallinity of carbon-based microstructures making up the array.

The present invention provides a fabrication method of an aggregate ofcarbon-based microstructures. The method includes the steps of: forminga plurality of carbon-based microstructures on a substrate with adirection of alignment perpendicular to the substrate; and pulling atleast one of the carbon-based microstructures.

Preferably, the fabrication method further includes the step ofsplitting the substrate, before the pulling step. This makes it easierto form the aggregate. It is preferable that the forming step beperformed by supplying the substrate with a source gas for forming thecarbon-based microstructures, and a carrier gas for carrying the sourcegas, and that a proportion of concentration of the source gas withrespect to a total concentration of the all gases is no less than 23%.In this way, density of the carbon-based microstructures formed on thesubstrate can be increased. This further improves ease of bundling andthe strength of the aggregate.

Preferably the fabrication method further includes the step ofphysically or chemically bonding the carbon-based microstructurestogether. In this way, the carbon-based microstructures can be firmlybonded together, and the strength of the aggregate can be furtherimproved.

The embodiments and concrete examples of implementation discussed in theforegoing detailed explanation serve solely to illustrate the technicaldetails of the present invention, which should not be narrowlyinterpreted within the limits of such embodiments and concrete examples,but rather may be applied in many variations within the spirit of thepresent invention, provided such variations do not exceed the scope ofthe patent claims set forth below. An embodiment based on a propercombination of technical means disclosed in different embodiments isencompassed in the technical scope of the present invention.

INDUSTRIAL APPLICABILITY

As described above, an aggregate of carbon-based microstructuresaccording to the present invention has various properties, includinghigh strength and high current density. Combined with the fact that theaggregate is observable by naked eye, these properties make theaggregate easy to handle and process. An aggregate of carbon-basedmicrostructures is therefore particularly suitable for small andlightweight electrical devices, wirings of such devices, and varioustypes of materials. As such, applicable fields of the present inventionare not just limited to industries manufacturing an aggregate ofcarbon-based microstructures, but the invention can be suitably used ina wide variety of industries, including chemical industry, materialprocessing, resin industry, and industries manufacturing electrical andelectronic devices and components, for example.

The invention claimed is:
 1. An aggregate of carbon-basedmicrostructures in which carbon nanotubes are assembled together,wherein the carbon nanotubes are aligned in one direction, and areassembled (i) along the direction of alignment so as to form a rope-likestructure having a length of not shorter than 20 cm by bundlingfilamentous structures, each of which is formed by bundling the carbonnanotubes, and (ii) in a direction orthogonal to the direction ofalignment so as to form a sheet-like structure, the carbon nanotubes aresurrounded by an amorphous carbon layer whose thickness is no greaterthan 10% of a diameter of the carbon nanotubes, the carbon nanotubeseach have a diameter of 10 nm through 20 nm, the carbon nanotubes areformed by a catalyst chemical vapor deposition method, using gas inwhich a proportion of concentration of a source gas for forming thecarbon nanotubes is no less than 23% of a total concentration, and theaggregate has a Young's modulus of not less than 0.8 TPa.
 2. Anaggregate of carbon-based microstructures as set forth in claim 1,wherein the carbon nanotubes include no greater than 10 bends per 1 μmlength extending in the direction of alignment.
 3. A resin sheet thatcomprises an aggregate of carbon-based microstructures set forth inclaim
 1. 4. A laminate that comprises one or more of the resin sheet setforth in claim
 3. 5. A high-temperature conducting sheet which comprisesthe laminate of claim
 4. 6. A high-temperature conducting sheet whichcomprises the resin sheet of claim
 3. 7. A film which comprises anaggregate of carbon-based microstructures set forth in claim
 1. 8. Afilm as set forth in claim 7, which is used as a transparentelectromagnetic wave absorber.
 9. An aggregate of carbon-basedmicrostructures as set forth in claim 1, wherein the carbon nanotubesare assembled (i) along the direction of alignment so as to form arope-like structure having a length of not shorter than 50 cm, and (ii)in the direction orthogonal to the direction of alignment so as to formthe sheet-like structure.
 10. An aggregate of carbon-basedmicrostructures as set forth in claim 1, wherein the carbon nanotubesare formed by a catalyst chemical vapor deposition method, using gas inwhich a proportion of concentration of a source gas for forming thecarbon nanotubes is no less than 28% of a total concentration.
 11. Anaggregate of carbon-based microstructures as set forth in claim 1,wherein the carbon nanotubes are formed by a catalyst chemical vapordeposition method, using gas in which a proportion of concentration of asource gas for forming the carbon nanotubes is no less than 70% of atotal concentration.
 12. An aggregate of carbon-based microstructures asset forth in claim 1, which is produced with a source gas, which issupplied only for a certain time period, and with a carrier gas, solelysupplied for other times, for carrying the source gas.
 13. An aggregateof carbon-based microstructures in which carbon nanotubes are assembledtogether, wherein the carbon nanotubes are aligned in one direction andare assembled together along the direction of alignment so as to form arope-like structure having a length of not shorter than 20 cm bybundling filamentous structures, each of which is formed by bundling thecarbon nanotubes, the carbon nanotubes are surrounded by an amorphouscarbon layer whose thickness is no greater than 10% of a diameter of thecarbon nanotubes, the carbon nanotubes each have a diameter of 10 nmthrough 20 nm, the carbon nanotubes are formed by a catalyst chemicalvapor deposition method, using gas in which a proportion ofconcentration of a source gas for forming the carbon nanotubes is noless than 23% of a total concentration, and the aggregate has a Young'smodulus of not less than 0.8 TPa.
 14. An aggregate of carbon-basedmicrostructures as set forth in claim 13, wherein the carbon nanotubesare assembled along the direction of alignment so as to form a rope-likestructure having a length of not shorter than 50 cm.
 15. An aggregate ofcarbon-based microstructures as set forth in claim 13, wherein thecarbon nanotubes include no greater than 10 bends per 1 μm lengthextending in the direction of alignment.
 16. A resin sheet thatcomprises an aggregate of carbon-based microstructures set forth inclaim
 13. 17. A film which comprises an aggregate of carbon-basedmicrostructures set forth in claim
 13. 18. A plied yarn-structure whichcomprises a ply of a plurality of aggregates set forth in claim
 13. 19.A fabric structure which comprises a resin-impregnated ply of aplurality of aggregates set forth in claim
 13. 20. An aggregate ofcarbon-based microstructures as set forth in claim 13, wherein thecarbon nanotubes are formed by a catalyst chemical vapor depositionmethod, using gas in which a proportion of concentration of a source gasfor forming the carbon nanotubes is no less than 28% of a totalconcentration.
 21. An aggregate of carbon-based microstructures as setforth in claim 13, wherein the carbon nanotubes are formed by a catalystchemical vapor deposition method, using gas in which a proportion ofconcentration of a source gas for forming the carbon nanotubes is noless than 70% of a total concentration.
 22. An aggregate of carbon-basedmicrostructures as set forth in claim 13, which is produced with asource gas, which is supplied only for a certain time period, and with acarrier gas, solely supplied for other times, for carrying the sourcegas.